I saw an M-18 hull parked in the weeds at the edge of a field in Germany back in 1981. It was pretty unique. The turret was missing and there was OD painted iron work added that looked like it was meant to support a wooden rail around the turret opening. The wood had long ago rotted away. I thought it might be a field conversion of an M-18 that had a damaged turret.
I described it to Nick and he built this model of it. It does look similar to the M-39 version of the M-18 hull.